The invention relates generally to passive samplers and more particularly to passive samplers with improved sampling efficiency for solid and liquid particles in air.
Gases and vapors are made up of very small molecules, on the order of angstroms. Because of the small size, gases and vapors have a high diffusion coefficient and move easily through the air. In contrast, aerosols are typically liquid droplets or solid particulates that are on the order of microns, thus they have a lower diffusion coefficient and tend to settle due to gravity instead of floating indefinitely like a vapor or gas. Clouds, dust storms, smoke, diesel exhaust, pollen, etc are all examples of aerosols. Biological particles such as bacteria and viruses can also form aerosols. Because of their different sizes and behaviors in the environment, particles in air require different sampling techniques than gases and vapors
There is a need for improved collection of particles from a variety of environments. Generally, there are two types of samplers, active and passive. In active sampling, airborne particles are actively collected by using pumps to pull aerosols through samplers that contain filters or other impaction surfaces. Active samplers are efficient in collecting particles because of the high airflow that can be achieved by a pump. Particles are collected using mechanisms such as impaction, interception, filtration, and diffusion. However, active samplers require a power source and some field locations may not have electricity. In addition, battery power may not be adequate for long sample durations. Another drawback of active samplers is the extra weight and noise for someone carrying a personal active sampler.
Due to the weight and noise of active samplers, passive sampling methods are often preferred for personal use. However, passive samplers are most effective for gasses and vapor because of their high diffusion coefficient. Although small particles in an aerosol may be sampled using a passive sampler, the sampling efficiency is low. Passive sampling of airborne particles may be accomplished by taking advantage of the settling feature of aerosol particles by placing Petri-dishes, microscope slides or sampling surfaces on the floor. Larger particles can be more efficiently collected by their settling; however, this is not a good method for smaller particles such as single spore bacteria and small clusters of bacteria. It can also require a long time period to gather sufficient particles for analysis. In addition, determining aerosol exposure to a person working in various locations requires a sampler placed on that person to accurately quantify the exposure to that person.
Thus, a need exists for a passive sampler that is convenient for personal use, and has a high sampling efficiency for the micron-sized particles typically found in an aerosol. Further, there is a need for a passive sampler that takes advantage of natural ambient air currents or air flows caused by motion of a person wearing the sampler. A passive sampler can also be attached to a moving object (vehicle) or attached to a stationary object in a moderate to high air flow environment.